COMET Report Summary

Process related parameters have been established for cordierite-based glass-ceramics with a view to developing substrate materials for microwave integrated circuits (MIC). The new materials combine low values of permittivity with low microwave losses. As a consequence, MICs become available with improved signal transmission characteristics.

Powders prepared by melting and sol-gel techniques were processed by cold pressing and sintering to bulk specimens with a well-suited property profile in density and dielectric parameters. Thin discs were cut from sintered blocks, polished and their metallization behaviour was studied for copper-based microwave lines. Resulting transmission characteristics were measured for coplanar line geometries. Drilling of electrical contact holes was established using a neodymium yttrium aluminium garnet (NdYAG) laser. Several approaches have been established for the sol-gel preparation of cordierite. One procedure was specially adapted to large-scale production (above 50 g). The sol-gel technique was also successfully applied for making ferro-electric materials with a wide compositional spectrum available. The technique gives the possibility of obtaining powders and thin films. The suitability of depositing these films on cordierite substrates was demonstrated as well as the potential in principle for depositing on other substrates like alumina and silicon. The processing and characterization of classical striplines was accomplished by establishing an appropriate thin film C copper u metallization technique for the cordierite substrates. Microwave characterization of the stripline performance was evaluated using simple line geometries, ring resonators and structures in a thin film multi-layer configuration. The processing and characterization of substrates with miniaturized elements resulted in a successful implementation of nickel chromium resistors. Ferroelectric capacitors were formed with the developed sol-gel materials Stable performance could only be demonstrated for ultra low roughness substrates (silicon).